EE on psychology and music

I'm doing my EE on the effect of music training (playing an instrument) on verbal ability. All the research I've found suggests that music training improves verbal ability and I cannot seem to find any research or study that suggests otherwise. Do I need a counter-argument or evidence against what all the research suggests in order to get full marks? I'm scared that if I don't have another side to it, my essay will suffer in the analysis/ discussion.